A pattern of serious injection drug user (IDU) driven HIV epidemics in Asia, with emerging evidence of generalization through heterosexual transmission, indicates the need for interventions focusing on both drug- and sex-related risk reduction. In a cross-border HIV prevention project for IDUs in northern Vietnam and southern China, peer educators disseminated risk reduction information to IDUs in the community and provided 20,000-25,000 sterile needles/syringes and 4,000-6,000 condoms per month. Since implementation of these interventions, the frequency of both injecting and sexual risk behaviours fell significantly, HIV prevalence among IDUs declined or stabilized, and HIV incidence dropped. There is official support for harm reduction interventions in both countries but this appears precarious in view of persistently powerful political and financial support for a law enforcement approach. Moreover, the simultaneous pursuit of inconsistent policies can have negative effects on the implementation of interventions. A harmonized and consistent policy environment is needed. Most of the evidence for efficacy of community-based HIV prevention comes from the developed world, but well-designed evaluations of such interventions in Asia and elsewhere in the developing world would have a better chance to influence policy decisions there. A synergistic approach to research, policy development, and service delivery is best calculated to achieve positive results in the struggle against HIV/AIDS in developing countries.